Hydraulic devices which have a series of expandable and contractible fluid chambers that are formed by an external toothed gerotor rotor that intermeshes with internal toothed stator during relative orbital and rotational movement are extensively used. The internal teeth of the stator are often constructed of cylindrically shaped rollers that are free to rotate in recesses in the stator while in engagement with a tooth of the rotor so as to seal a high pressure zone of the hydraulic device from a low pressure zone. The external toothed rotor, or star gear, has one less tooth than the internal toothed stator, or ring gear. The star gear thus partakes of a hypocycloidal movement so that the axis of the star gear travels in orbit above the axis of the internal ring gear.
A machine for accurately testing the profile of the external toothed rotor was developed and is disclosed in United States patent application Ser. No. 793,976 which is assigned to the assignee of the present invention and was filed in the name of Henry J. Flair. Although go and no go gages conceivably might be used to determine whether or not an internal toothed stator was within allowed tolerances in a gerotor mechanism, these gages would be of limited utility and accuracy since they would not have the shape of the external toothed rotor, and they will not be capable of detecting the source of any interference errors that may exist. The use of a master gear having the shape of a gerotor rotor is not possible, however, because when an external toothed rotor is inserted into the internal toothed stator of a gerotor device the overlap is such that the variation in the center-to-center distance between the centers of the rotor and the stator can not be detected.
The present invention is directed to an external toothed rotor that serves as a master gear and that has a tooth form which is modified from that of an operating star gear rotor. A mechanism for centering and quick release holding of the internal toothed stator on an arbor of a rotatable support member, so that the star gear rotor rotates about its center as the ring gear rotates about its center, is also provided. The external toothed rotor is positioned relative to the internal toothed stator so that the centers of the rotor and the stator remain positioned along the same lines at all times. With the rotor center being fixed and the stator center being slidable along this line, a measuring device can be coupled to detect the motion of the stator relative to the rotor thereby indicating the magnitude of manufacturing variations of the internal toothed stator from an ideal stator.
Prior to the present invention, it was customary to assemble the internal and external tooth gears together and to operate the device to see if satisfactory operation was obtainable, and if not, to disassemble the device. Sometimes this same rotor and stator would be used in a different assembly to see if they might work in combination with a new mating gear. The present invention provides a means of accurately predicting the operation of an internal toothed gear with respect to an external toothed rotor, so as to thereby eliminate repeated assembly and disassembly operations in the manufacture of gerotor devices.